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PubMed2005

The sulfide binding function of annelid hemoglobins: relic of an old biosystem?

Invertebrates living in sulfide-rich environments have developed different strategies of coping with sulfide toxicity. Some bivalves and annelids have hemoglobins that are capable of binding sulfide for detoxification and/or transporting it to internal bacterial symbionts. Annelids living in the sulfide-rich environments have giant (approximately 3.6 MDa) hemoglobin, consisting of 144 globin chains arranged in a hexagonal bilayer structure held together by 36 nonglobin linker chains. Some globin chains contain either a free cysteine residue at positions Cys+1 or at position Cys+11 relative to the E7 distal residue in the E helix and EF interhelical region, respectively, which bind sulfide. The hexagonal bilayer hemoglobins of annelids living in environments lacking sulfide, do not have the corresponding free cysteine residues and cannot bind sulphide. Given that the early stages of life occurred under anoxic conditions in the presence of sulfide, it is possible that the sulfide binding function from modern annelid globins inhabiting sulphide rich habitats is an evolutionary relic. This proposal seems supported by the recent finding of "protoglobins" which also have a corresponding cysteine residue in Archea known to exist in hyperthermophilic and sulfide-rich environments.

Amino Acid Sequence↗
PubMed2002

Kinetics of chemical decolorization of the azo dye C.I. Reactive Orange 96 by sulfide.

The mechanism of decolorization of azo dyes based on the extracellular chemical reduction with sulfide (H2S, HS-, S2-) was postulated for sulfate reducing environments. To design technical decolorization processes of textile wastewater treatment with sulfide produced by sulfate reducing bacteria (SRB), kinetics is of great significance. Batch experiments were made in order to investigate the kinetics of abiotic decolorization of the reactive mono-azo dye C.I. Reactive Orange 96 (RO 96) with sulfide, with varying pH. The decolorization of RO 96 by sulfide under the exclusion of O2 corresponded to first-order kinetics with respect to both dye and sulfide concentration. The decolorization of RO 96 with sulfide at neutral pH (7.1) was advantageous compared with that at pH for 4.1, 6.3, and 6.5. This is attributed to an increase in the fraction of HS- of total sulfide species at neutral pH. The rate constants k for the decolorization at 37 degrees C were obtained as 0.01 for pH = 4.1, 0.06 for pH = 6.3, 0.08 for pH = 6.5, and 0.09 for pH = 7.1 in mM(-1) min(-1). The high rate constants for sulfide at pH 6.5-7.1 support that the decolorization through SRB (i.e. by bio-sulfide) can be effective in anaerobic bacterial systems with sulfate.

Azo Compounds↗
PubMed2002

Use of hydrochloric acid for determinining solid-phase arsenic partitioning in sulfidic sediments.

We examined the use of room-temperature hydrochloric acid (1-6 M) and salt solutions of magnesium chloride, sodium carbonate, and sodium sulfide for the removal of arsenic from synthetic iron monosulfides and contaminated sediments containing acid-volatile sulfides (AVS). Results indicate that acid-soluble arsenic reacts with H2S released from AVS phases and precipitates at low pH as disordered orpiment or alacranite. Arsenic sulfide precipitation is consistent with geochemical modeling in that conditions during acid extraction are predicted to be oversaturated with respect to orpiment, realgar, or both. Binding of arsenic with sulfide at low pH is sufficiently strong that 6 M HCl will not keep spiked arsenic in the dissolved fraction. Over a wide range of AVS concentrations and molar [As]/[AVS] ratios, acid extraction of arsenic from sulfide-bearing sediments will give biased results that overestimate the stability or underestimate the bioavailability of sediment-bound arsenic. Alkaline solutions of sodium sulfide and sodium carbonate are efficient in removing arsenic from arsenic sulfides and mixed iron-arsenic sulfides because of the high solubility of arsenic at alkaline pH, the formation of stable arsenic complexes with sulfide or carbonate, or both.

Arsenic↗
PubMed2004

Effect of sodium sulfide on Ni-containing carbon monoxide dehydrogenases.

The structure of the active-site C-cluster in CO dehydrogenase from Carboxydothermus hydrogenoformans includes a mu(2)-sulfide ion bridged to the Ni and unique Fe, whereas the same cluster in enzymes from Rhodospirillum rubrum (CODH(Rr)) and Moorella thermoacetica (CODH(Mt)) lack this ion. This difference was investigated by exploring the effects of sodium sulfide on activity and spectral properties. Sulfide partially inhibited the CO oxidation activity of CODH(Rr) and generated a lag prior to steady-state. CODH(Mt) was inhibited similarly but without a lag. Adding sulfide to CODH(Mt) in the C(red1) state caused the g(av) = 1.82 EPR signal to decline and new features to appear, including one with g = 1.95, 1.85 and (1.70 or 1.62). Removing sulfide caused the g(av) = 1.82 signal to reappear and activity to recover. Sulfide did not affect the g(av) = 1.86 signal from the C(red2) state. A model was developed in which sulfide binds reversibly to C(red1), inhibiting catalysis. Reducing this adduct causes sulfide to dissociate, C(red2) to develop, and activity to recover. Using this model, apparent K(I) values are 40 +/- 10 nM for CODH(Rr) and 60 +/- 30 microM for CODH(Mt). Effects of sulfide are analogous to those of other anions, including the substrate hydroxyl group, suggesting that these ions also bridge the Ni and unique Fe. This proposed arrangement raises the possibility that CO binding labilizes the bridging hydroxyl and increases its nucleophilic tendency toward attacking Ni-bound carbonyl.

Aldehyde Oxidoreductases↗
PubMed1998

Technological aspects of the microbial treatment of sulfide-rich wastewaters: a case study.

Thiobacillus denitrificans has been shown to be an effective biocatalyst for the treatment of a variety of sulfide-laden waste streams including sour water, sour gases, and refinery spent-sulfidic caustics. The term 'sour' originated in the petroleum industry to describe a waste contaminated with hydrogen sulfide or salts of sulfide and bisulfide. The microbial treatment of sour waste streams resulting from the production or refining of natural gas and crude oil have been investigated in this laboratory for many years. The application of this technology to the treatment of sour wastes on a commercially useful scale has presented several technical barriers including substrate inhibition (sulfide), product inhibition (sulfate), the need for septic operation, biomass recycle and recovery, mixed waste issues, and the need for large-scale cultivation of the organism for process startup. The removal of these barriers through process improvements are discussed in terms of a case study of the full-scale treatment of sulfide-rich wastewater. The ability of T. denitrificans to deodorize and detoxify an oil-field produced water containing sulfides was evaluated under full-scale field conditions at Amoco Production Co. Salt Creek Field in Midwest, WY. More than 800 m3/d of produced water containing 100 mg/L sulfide and total dissolved solids of 4800 mg/L were successfully biotreated in an earthen pit (3000 m3) over a six-month period. Complete removal of sulfides and elimination of associated odors were observed. The system could be upset by severe hydraulic disturbances; however, the system recovered rapidly when normal influent flow rates were restored.

Biodegradation, Environmental↗
PubMed2002

Effect of initial periodontal therapy on sulcular/tongue sulfide level. A pilot study.

BACKGROUND: : Volatile sulfur compounds (VSC), such as hydrogen sulfide, methyl mercaptan and dimethyl sulfide, are toxic metabolites produced by periodontal pathogens. These VSC are also released from the tongue dorsum. Currently, limited data are available on how periodontal treatments may affect sulcular/tongue sulfide level. The aim of this study was to determine effect of initial therapy including oral hygiene instruction and scaling and root planing (SRP) on sulcular/tongue sulfide level. METHODS: : Thirteen subjects diagnosed with chronic periodontitis and having three representative periodontal pocket depth (PD) strata in one quadrant (PD or= 7.0 mm: severe disease sites) were selected. Clinical periodontal parameters were recorded at baseline and 3 weeks after completion of the initial therapy. The sulfide levels in three representative periodontal pockets (pS) and on three parts (anterior, middle, and posterior) of the tongue dorsum (tS) were measured using a commercial sulfide-monitoring device. RESULTS: : The pS levels of the three representative sites were reduced significantly following the initial therapy (p < 0.05). However, there was no significant reduction of the tS level in all three parts of the tongue. CONCLUSIONS: : The initial periodontal therapy such as oral hygiene and SRP reduces the sulcular sulfide level but not the tongue sulfide level. This suggests that sulcular sulfide level may be a possible indicator for assessing the outcome of initial periodontal treatment.

Adult↗
PubMed1999

Anaerobic versus aerobic degradation of dimethyl sulfide and methanethiol in anoxic freshwater sediments.

Degradation of dimethyl sulfide and methanethiol in slurries prepared from sediments of minerotrophic peatland ditches were studied under various conditions. Maximal aerobic dimethyl sulfide-degrading capacities (4.95 nmol per ml of sediment slurry. h-1), measured in bottles shaken under an air atmosphere, were 10-fold higher than the maximal anaerobic degrading capacities determined from bottles shaken under N2 or H2 atmosphere (0.37 and 0. 32 nmol per ml of sediment slurry. h-1, respectively). Incubations under experimental conditions which mimic the in situ conditions (i. e., not shaken and with an air headspace), however, revealed that aerobic degradation of dimethyl sulfide and methanethiol in freshwater sediments is low due to oxygen limitation. Inhibition studies with bromoethanesulfonic acid and sodium tungstate demonstrated that the degradation of dimethyl sulfide and methanethiol in these incubations originated mainly from methanogenic activity. Prolonged incubation under a H2 atmosphere resulted in lower dimethyl sulfide degradation rates. Kinetic analysis of the data resulted in apparent Km values (6 to 8 microM) for aerobic dimethyl sulfide degradation which are comparable to those reported for Thiobacillus spp., Hyphomicrobium spp., and other methylotrophs. Apparent Km values determined for anaerobic degradation of dimethyl sulfide (3 to 8 microM) were of the same order of magnitude. The low apparent Km values obtained explain the low dimethyl sulfide and methanethiol concentrations in freshwater sediments that we reported previously. Our observations point to methanogenesis as the major mechanism of dimethyl sulfide and methanethiol consumption in freshwater sediments.

Aerobiosis↗
PubMed2000

In situ determination of sulfide turnover rates in a meromictic alpine lake.

A push-pull method, previously used in groundwater analyses, was successfully adapted for measuring sulfide turnover rates in situ at different depths in the meromictic Lake Cadagno. In the layer of phototrophic bacteria at about 12 m in depth net sulfide consumption was observed during the day, indicating active bacterial photosynthesis. During the night the sulfide turnover rates were positive, indicating a net sulfide production from the reduction of more-oxidized sulfur compounds. Because of lack of light, no photosynthesis takes place in the monimolimnion; thus, only sulfide formation is observed both during the day and the night. Sulfide turnover rates in the oxic mixolimnion were always positive as sulfide is spontaneously oxidized by oxygen and as the rates of sulfide oxidation depend on the oxygen concentrations present. Sulfide oxidation by chemolithotrophic bacteria may occur at the oxicline, but this cannot be distinguished from spontaneous chemical oxidation.

Bacteria↗
PubMed1985

Potentiation by sulfide of hydrogen peroxide-induced killing of Escherichia coli.

L-Cysteine potentiates 100-fold the hydrogen peroxide-induced killing of a growing culture of Escherichia coli K-12 (Berglin et al., J. Bacteriol. 152:81-88). In the present study it is shown that hydrogen sulfide is formed from L-cysteine and that sodium sulfide could substitute for L-cysteine in the potentiation of hydrogen peroxide-induced killing of E. coli K-12. Addition of an amino acid, L-leucine, L-valine, or L-alanine, to an L-cysteine-containing medium with a growing culture of E. coli K-12 inhibited hydrogen sulfide formation and the potentiation of hydrogen peroxide-induced killing. These amino acids did not inhibit hydrogen sulfide formation from L-cysteine by a cell extract, and they did not inhibit the potentiation by sulfide of hydrogen peroxide-induced killing. This indicated that the amino acids protected the culture from L-cysteine-potentiated, hydrogen peroxide-induced killing by inhibiting the transport of L-cysteine into the cell. The potentiation by sodium sulfide of hydrogen peroxide-induced killing was abolished by the metal ion chelator 2,2'-bipyridyl. This indicated that metal ions, in addition to sulfide, were involved in the killing. Toxic effects of hydrogen peroxide are often presumed to be mediated by hydroxyl radicals formed in iron-catalyzed reactions. It was demonstrated that iron sulfide was more efficient than ferrous iron in catalyzing the formation of hydroxyl radicals from hydrogen peroxide. It was suggested that hydrogen sulfide formed in polymicrobial infections may play an important role in the host defense by potentiating the antimicrobial effect of hydrogen peroxide produced by phagocytic cells.

Cysteine↗
PubMedDate not supplied

Air-water transfer of hydrogen sulfide: an approach for application in sewer networks.

The emissions process of hydrogen sulfide was studied to quantify air-water transfer of hydrogen sulfide in sewer networks. Hydrogen sulfide transfer across the air-water interface was investigated at different turbulence levels (expressed in terms of the Froude number) and pH using batch experiments. By means of the overall mass-transfer coefficient (KLa), the transfer coefficient of hydrogen sulfide (KLa(H2S)), referring to total sulfide, was correlated to that of oxygen (KLa(O2)) (i.e., the reaeration coefficient). Results demonstrate that both turbulence and pH in the water phase play a significant role for KLa(H2S). An exponential expression is a suitable representation for the relationship between KLa(H2S) and the Froude number at all pH values studied (4.5 to 8.0). Because of the dissociation of hydrogen sulfide. KLa(H2S) increased with decreasing pH at a constant turbulence level. Relative differences in KLa(H2S) at pH values between 4.5 and 8.0 became larger as the turbulence level increased, whereas those at pH between 4.5 and 7.0 did not statistically show any change. At constant pH, KLa(H2S)/KLa(O2) was observed not to be dependent on the turbulence range studied. KLa(H2S)/ KLa(O2) ratio was 0.86, with a 95% confidence interval of 0.08 at low pH, where only molecular hydrogen sulfide was present. This ratio was found to be equal to the ratio between the diffusion coefficient of hydrogen sulfide and that of oxygen. which was determined by empirical equations proposed in the literature. This fact was observed at all the turbulence levels investigated. Based on the findings in this study, an empirical equation describing the pH dependence of KLa(H2S)/KLa(O2) at a pH range of 4.5 to 8.0 is proposed. Theoretical and experimental aspects of hydrogen sulfide emissions and an application are discussed related to in-sewer conditions.

Air↗
PubMed2002

Fatal and nonfatal poisoning by hydrogen sulfide at an industrial waste site.

An adult man (A) entered a pit to collect seepage at an industrial waste site in Japan. As he suddenly lost consciousness, three colleagues (B, C, D) entered the pit to rescue him. All of these men lost consciousness in the pit. Two workers (A and B) died soon after the accident, one worker (C) died 22 days after the accident, and one worker (D) survived. Since hydrogen sulfide gas was detected in the atmosphere of the pit, gas poisoning was suspected. Toxicological analyses of sulfide and thiosulfate, a metabolite of sulfide, in blood and urine of the victims were made using the extractive alkylation technique combined with gas chromatography/mass spectrometry (GC/MS). Sulfide was detected in the blood of A and B at levels of 0.13 and 0.11 mg/L, respectively, somewhat higher than in healthy persons. Thiosulfate was detected in whole blood of deceased victims A and B, in the plasma of deceased victim C, at concentrations of 10.53, 4.59, and 4.14 mg/L, respectively. These values were similar to those found in fatal cases of hydrogen sulfide poisoning. Thiosulfate was not detected in the plasma of survivor D. With respect to urine samples, thiosulfate was the highest in the non-acute death victim C (137.20 mg/L), followed by that in the survivor D (29.34 mg/L), and low (0.90 mg/L) and not detected in the acute death victims, A and B, respectively. Based on these results, all four patients were victims of hydrogen sulfide poisoning. The concentrations of thiosulfate in blood and urine were more useful than that for sulfide for determining hydrogen sulfide poisoning. Thiosulfate in urine was the only indicator of hydrogen sulfide poisoning in the non-fatal victim.

Fatal Outcome↗
PubMed1993

The oral antihypertensive activity of the methylated derivatives of phenyl-2-aminoethyl sulfide.

We have reported previously that phenyl-2-aminoethyl sulfide and its derivatives are excellent substrates for dopamine-beta-monooxygenase and produce an antihypertensive effect in spontaneously hypertensive rats after i.p. administration. In the studies reported herein, we demonstrate that alpha-methyl-phenyl-2-aminoethyl sulfide and 4-hydroxy-alpha-methyl-phenyl-2-aminoethyl sulfide, the methylated and hydroxymethylated derivatives of phenyl-2-aminoethyl sulfide, respectively, decrease mean arterial pressure in conscious, unrestrained spontaneously hypertensive rats after p.o. administration. This antihypertensive effect after p.o. administration occurs without the undesirable transient rise in blood pressure observed previously after i.p. administration. Results using the methodology of food-reinforced operant conditioned behavior are consistent with the interpretation that the ring hydroxylated derivatives, 4-hydroxy-phenyl-2-aminoethyl sulfide and 4-hydroxy-alpha-methyl-phenyl-2-aminoethyl sulfide, do not penetrate into the central nervous system. This finding supports our contention that the primary site of action for the antihypertensive activity of the sulfides may be the peripheral adrenergic nerve ending. In view of the current high degree of interest in chiral development, the enantiomeric specificity of the antihypertensive activity of alpha-methyl-phenyl-2-aminoethyl sulfide was also evaluated. Results from these studies demonstrate that the (S)-enantiomer of alpha-methyl-phenyl-2-aminoethyl sulfide is more effective in lowering blood pressure after p.o. administration than the (R)-enantiomer. The implications of our findings in terms of the mechanism of action of these compounds are discussed.

Administration, Oral↗
PubMed1995

Comparison of 1% and 2.5% selenium sulfide in the treatment of tinea capitis.

OBJECTIVE: To determine whether an over-the-counter shampoo containing 1% selenium sulfide would have sporicidal activity equal to that of a 2.5% selenium sulfide prescription lotion in the adjunctive treatment of tinea capitis infection. DESIGN: Prospective randomized nonblinded clinical trial. SETTING: Outpatient clinics and emergency department of a children's hospital. PATIENTS: Fifty-four patients between the ages of 1 and 15 years with culture-proved tinea capitis infection caused by Trichophyton tonsurans enrolled during a 14-month period. METHODS: Patients were randomized to receive 2.5% selenium sulfide lotion, 1% selenium sulfide shampoo, or a bland, nonmedicated shampoo with which they were instructed to shampoo twice weekly. All received 15 mg/kg per day of griseofulvin. Dermatophyte cultures of the affected area of each patient's scalp were obtained on enrollment and every 2 weeks until a negative culture was obtained from a previously infected area. RESULTS: Survival data analysis demonstrated that both the 2.5% selenium sulfide and 1% selenium sulfide preparations were superior to the nonmedicated control shampoo in terms of the time required to eliminate shedding of viable spores. When compared with each other, there was no difference between the 2.5% selenium sulfide and 1% selenium sulfide preparations in time required to produce a negative culture. CONCLUSION: Commercially available 1% selenium sulfide shampoo is an equally effective yet less expensive alternative sporicidal therapy in the adjunctive treatment of tinea capitis infection.

Adolescent↗
PubMed1999

Use of nitrate to control sulfide generation by sulfate-reducing bacteria associated with oily waste.

Sulfide is a toxic and corrosive product of sulfate-reducing bacteria that can accumulate in oily waste streams to nuisance levels. Sludge associated with an oily waste stream was collected from a settling tank and used to assess sulfide generation activities. Methanogenesis was a predominant process in sludge in the absence of sulfate, and was suppressed by nitrate. Sulfate reduction and sulfide formation were evident when sulfate was available. Nitrate diminished sulfate reduction and prevented sulfide accumulation under freshwater, brackish, and saltwater conditions. Sodium-, potassium-, and calcium nitrate were equally effective in curtailing sulfide formation. The effects of nitrate on sulfate depletion were concentration-dependent, with 50 mM nitrate diminishing sulfate reduction, yet as little as 16 mM nitrate prevented sulfide accumulation. Sulfide was oxidized in nitrate-reducing incubations, and accumulation of sulfur or sulfate was observed. Nitrate reduction was accompanied by production of nitrite and nitrous oxide, which probably helped prevent sulfate reduction in extended incubations. Our results suggest that nitrate amendments control the formation of sulfide in oily waste streams both by preventing sulfate reduction and by stimulating anaerobic sulfide oxidation.

Journal Article↗
PubMed1983

Na-Dithionite Promotes Photosynthetic Sulfide Utilization by the Cyanobacterium Oscillatoria limnetica.

The light- and sulfide-dependent induction process leading to photosystem I-mediated sulfide utilization by Oscillatoria limnetica, for either H(2) evolution or CO(2) photoassimilation, was studied. The identical dependence on pH of the lag length, the inhibition of leucine incorporation and final H(2)S concentration imply that the latter exerts a deleterious effect on nonadapted cells.Na-dithionite (Na(2)S(2)O(4)), Na-sulfite (Na(2)SO(3)), or ethanol cannot serve as photosynthetic electron donors. However, when these compounds were added to the sulfide-containing system, the need for induction was eliminated. At pH 6.9, in the presence of 3.5 millimolar sulfide, these substances (at concentrations of 10 millimolar, 5 millimolar, or 0.4 molar, respectively) completely abolished the delay preceding sulfide-dependent H(2) evolution. It is suggested that all three compounds expose a site capable of directly accepting sulfide electrons.Only dithionite could adapt the cells to sulfide utilization on its own. Sulfite or ethanol acted only in the presence of sulfide. It is implied that this specific activity of dithionite is related to its characteristic low redox potential.Sulfide-dependent H(2) evolution was insensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea, but was inhibited by the plastoquinone antagonist 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, in the presence as well as in the absence of dithionite. In both cases, therefore, the plastoquinone was implied in the electron transport from sulfide.

Journal Article↗
PubMed2025

Comparative Embryology and Transcriptomics of Asellus infernus, an Isopod Crustacean From Sulfidic Groundwater.

Sulfidic caves are harsh and extreme environments characterized by limited oxygen, low pH, and the presence of hydrogen sulfide. Amazingly, animals can live in sulfidic caves, one such animal being Asellus infernus, a representative of the Asellus aquaticus species complex, originating from Movile Cave and from old wells that represent windows of access to a sulfidic groundwater ecosystem located in southeast Romania. Little previous work has been done on lab-reared populations of A. infernus as they have been historically difficult to raise in the lab. Here, we develop resources for A. infernus, examining questions of timing of morphological differences in cave versus surface individuals, whether the environment (lab-bred vs. wild-caught) influenced size characteristics, and the genes and pathways showing differential expression between cave and surface samples. We found that A. infernus did not develop pigmentation embryonically, and juveniles had increased body length and longer antenna II as compared to surface individuals. Furthermore, we found that some of these measures differed between wild-caught and lab-reared juveniles for a given population, indicating that environmental differences can also influence these size characteristics. In addition, differential expression between cave and surface samples and allele-specific expression studies within F1 hybrids identified multiple genes, including those involved in sulfide metabolism and phototransduction. Strikingly, molecular convergence of genes involved in sulfide detoxification was observed between A. infernus and previous work on a fish that lives in both cave and sulfidic environments, Poecilia mexicana. In sum, we were able to develop embryonic and genomic tools for A. infernus, a model for understanding cave adaptation and adaptation to sulfidic environments.

Animals↗
PubMed2006

Kinetics and stoichiometry of aerobic sulfide oxidation in wastewater from sewers-effects of pH and temperature.

Kinetics and stoichiometry of aerobic chemical and biological sulfide oxidation in wastewater from sewer networks were studied. In this respect, the effects of temperature and pH were investigated in the ranges 10 to 20 degrees C and 5 to 9, respectively. The temperature dependency of sulfide oxidation kinetics was described using an Arrhenius relationship. The effect of pH on the rate of chemical sulfide oxidation is related to the dissociation of hydrogen sulfide (H2S) to hydrogen sulfide ion (HS(-)), with HS(-) being more readily oxidized than H2S. Biological sulfide oxidation exhibited the highest rates at ambient wastewater pH, and the reaction was inhibited at both low and high pH values. Chemical sulfide oxidation was found to produce thiosulfate and sulfate, while elemental sulfur was the main product of biological sulfide oxidation. Based on the investigations, general rate equations and stoichiometric constants were determined, enabling the processes to be incorporated to conceptual sewer process models.

Aerobiosis↗
PubMed2004

Reconsidering the use of photosynthetic bacteria for removal of sulfide from wastewater.

The feasibility of using photosynthetic sulfide-oxidizing bacteria to remove sulfide from wastewater in circumstances where axenic cultures are unrealistic has been completely reconsidered on the basis of known ecophysiological data, and the principles of photobioreactor and chemical reactor engineering. This has given rise to the development of two similar treatment concepts relying on biofilms dominated by green sulfur bacteria (GSB) that develop on the exterior of transparent surfaces suspended in the wastewater. The GSB are sustained and selected for by radiant energy in the band 720-780 nm, supplied from within the transparent surface. A model of one of these concepts was constructed and with it the reactor concept was proven. The dependence of sulfide-removal rate on bulk sulfide concentration has been ascertained. The maximum net areal sulfide removal rate was 2.23 g m-(2) day-(1) at a bulk sulfide concentration of 16.5 mg L(-1) and an incident irradiance of 1.51 W m(-2). The system has a demonstrated capacity to mitigate surges in sulfide load, and appears to use much less radiant power than comparable systems. The efficacy with which this energy was used for sulfide removal was 1.47 g day(-1) W(-1). The biofilm was dominated by GSB, and evidence gathered indicated that other types of phototrophs were not present.

Biodegradation, Environmental↗